Waveguided laser channels for a gas laser

ABSTRACT

An RF-excited waveguide laser module comprises a first electrode having a first elongate surface defining in part a waveguide laser channel extending along an optical axis, the first elongate surface having a substantially linear cross-section normal to the optical axis. A second electrode has a second elongate surface defining in part the waveguide laser channel extending along the optical axis. The second elongate surface has a non-linear cross-section normal to the optical axis. A dielectric insert may be provided between the electrodes defining in part the waveguide laser channel. A lengthwise gap may extend essentially an entire length of the waveguide laser channel between one of the first and second electrodes and the dielectric insert. The gap provides fluid communication between the waveguide laser channel and a volume outside the waveguide laser channel.

RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/778,513, filed Mar. 1, 2006, entitled “ImprovedMethod of Assembling RF-Excited Waveguide Gas Lasers and Improved WaveGuiding Laser Channels,” which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention is directed to RF-excited waveguide gas lasers andmore particularly, to improved waveguide laser channels.

BACKGROUND OF THE INVENTION

RF-excited waveguide gas lasers are finding more applications as theirreliability improves and their costs decrease. One of the keys toimproving reliability is eliminating the presence of any particles whichmay intrude in the waveguide laser channels and smash into and damagethe laser optics. One typical RF-excited waveguide laser assembly isdescribed in Hart, U.S. Pat. No. 6,192,061. The RF-excited waveguidelaser assembly of Hart consists of a pair of electrodes with dielectricwaveguide insert sandwiched therebetween. Hart includes a pair ofsprings 26 which maintain the sandwich assembly in its desiredconfiguration. One problem with a waveguide laser assembly as taught inHart is the springs 26 as well as the sandwich assembly are slid into ahousing interior and the lateral movement between the spring, thesandwiched assembly and the housing interior can generate particleswhich later can damage the optics in the manner described above.

Yet another problem with existing RF-excited waveguide gas lasers isthat harmonic acoustic resonance during pulsed operation within thewaveguide laser channels can adversely affect laser performance. Hart,U.S. Pat. No. 6,192,061 teaches providing a number of openings in thewaveguide laser channel at positions about where a pressure peak of anacoustic resonance would be located. More particularly, Hart teachesproviding such openings at about ¼, ½ and ¾ the lengths of each segmentof a waveguide laser channel. These openings are provided substantiallytransverse to the optical axis of the waveguide laser channels. Whilesuch openings may be somewhat effective in diminishing harmonic acousticresonance by venting gas from the waveguide channel, the openingsprovide only limited gas venting and fail to provide a suitable exit forparticles that may intrude the waveguide laser channels, thus increasingthe likelihood that any such particle will damage the waveguide optics.

Yet another known problem with existing RF-exited waveguide gas lasersis the waveguide laser channels are not configured to maximize higherorder mode suppression while simultaneously maximizing uniform dischargeformation.

The present invention is directed toward overcoming one or more of theproblems discussed above.

SUMMARY OF THE INVENTION

A first aspect of the invention is a method of making an RF-excitedwaveguide laser module that includes sandwiching a dielectric waveguideinsert between a first and a second electrode. The dielectric waveguideinsert and the first and second electrodes are secured together in asandwiched configuration to form a waveguide laser assembly. Thewaveguide laser assembly is inserted into a cavity of a housing withoutcontacting an interior surface of the cavity. The first electrode isthen brought into abutment with an inner surface of the cavity in adirection substantially normal to the inner surface of the cavity. Thewaveguide laser assembly is then secured within the housing cavity withonly the first electrode contacting an inner surface of the cavity. Inthe abutting and the securing steps, substantially no lateral movementoccurs between the first electrode and the inner surface of the cavity.The first electrode has a substantially planar surface abutting theinner surface of the cavity and the inner surface of the cavity islikewise planar. The securing step may be accomplished by providing aplurality of holes in the wall of the housing defining the inner surfaceof the housing and providing a corresponding plurality of internallythreaded holes in the first electrode. These holes are aligned andscrews are inserted to secure the waveguide laser assembly within thehousing.

A second aspect of the invention is an RF-excited waveguide gas lasermodule comprising a first electrode having a first elongate surfacedefining in part a waveguide laser channel extending along an opticalaxis, the first elongate surface having a substantially linearcross-section normal to the optical axis. A second electrode having asecond elongate surface defining in part the waveguide laser channelalso extends along the optical axis. The second elongate surface has anon-linear cross section normal to the optical axis. In one embodiment,non-linear cross-section may be arcuate. In one embodiment, thenon-linear surface is concave and has a distance between a bottom of theconcave surface and a top of the surface of between about 0.005-0.03inch, which equates to a radius of between about 0.0825-0.4 inch. Adielectric insert may be provided between the electrodes and in partdefine the waveguide laser channel. A lengthwise gap may extendessentially an entire length of the waveguide laser channel between oneof the first and second electrodes and the dielectric insert with thegap providing fluid communication between the waveguide laser channeland a volume outside the waveguide.

Yet another aspect of the invention is a waveguide gas laser comprisinga first electrode and a second electrode. A dielectric insert issandwiched between the ground electrode and the active electrode. Awaveguide channel is defined by at least one of the dielectric insert,the active electrode and the ground electrode. A lengthwise gap extendsessentially an entire length of the waveguide laser channel, thelengthwise gap providing fluid communication between the waveguide laserchannel and a volume outside the waveguide laser channel.

Yet another aspect of the invention is a first electrode having a firstelongate surface defining in part a waveguide laser channel extendingalong an optical axis. A second electrode has a second elongate surfacedefining in part the waveguide laser channel extending along the opticalaxis. A dielectric insert is sandwiched between the first and secondelectrodes, the dielectric insert comprising an elongate slot extendingalong the optical axis having side walls defining in part the waveguidelaser channel. A lengthwise gap extends essentially an entire length ofthe waveguide laser channel between at least one of the first and secondelectrode surfaces and the dielectric insert, the gap providing fluidcommunication between the waveguide laser channel and a volume outsidethe waveguide laser channel.

The RF-excited waveguide gas laser module in accordance with the presentinvention has a waveguide channel which maximizes higher order modesuppression and maximizes uniform discharge formation. The waveguidechannel in accordance with the present invention further providesexcellent gas venting to eliminate acoustical distortion. The elongategaps incorporated into the waveguide channel provide a particle exit outof the waveguide channel to minimize the likelihood of damage to thelaser optics in the event a particle intrudes into the waveguidechannel. The metal to metal electrode surfaces found on opposing sidesof the waveguide channel provide good plasma breakdown. These manyadvantages are provided in an RF-excited waveguide gas laser module thatcan be efficiently assembled from conventional materials. The assemblymethod described herein minimizes the chance of particle formation,enhancing reliability and service lifetime. The higher reliabilitygreatly enhances the economic viability of the RF-excited waveguide gaslaser module.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a partially assembled RF-excitedwaveguide gas laser module in accordance with the present invention;

FIG. 2 is an exploded view of the RF-excited waveguide gas laser moduleand waveguide laser assembly of FIG. 1;

FIG. 3 is a cross-section of the RF-excited waveguide gas laser of FIG.1 taken along line AA of FIG. 1;

FIG. 4 is a cross-section of the RF-excited waveguide gas laser of FIG.1 taken along line BB of FIG. 1;

FIG. 5 is a perspective view of the active electrode of the presentinvention;

FIG. 6 is an enlarged portion of wave guiding laser channel illustratedin FIG. 3;

FIG. 7 is a schematic representation of a jig for supporting thewaveguide laser assembly for insertion into a cavity of a housingwithout contacting an inner surface of the cavity; and

FIG. 8 is a schematic representation of the RF field formed within thewaveguide channel of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A partially assembled RF-excited waveguide gas laser module 10 isillustrated in FIG. 1. The module 10 comprises a housing 12 containing awaveguide laser assembly 14 shown exploded in FIG. 2. An end panel 16 isshown removed from the housing to reveal optic adjustment plates 18having holes 20 for accessing optics adjustment screws as known in theart. A heat sink 22 is shown attached in abutment to a top surface 24 ofthe housing 12. Screw holes 26 are also provided in the top surface 24of the housing 12 for attaching other heat sinks, which are not shownfor the sake of clarity.

Referring to FIG. 2, the waveguide laser assembly 14 is shown explodedand removed from a cavity 30 of the housing 12. The waveguide laserassembly 14 comprises a first electrode 32, a second electrode 34 and adielectric insert assembly 36. Either or both electrodes could be activeor “hot”. However, in the embodiment discussed herein the secondelectrode is the active electrode and the first electrode is a groundelectrode. Once assembled in a sandwiched configuration which will bedescribed in greater detail below, the first electrode 32, the secondelectrode 34 and the dielectric insert assembly 36 collectively define aZ-shaped waveguide laser channel 38 which is best viewed in FIG. 4.While a Z-shaped channel 38 is expressly disclosed, other configurationsor courses of the channel could be substituted and are considered withinthe scope of the invention. Some such configurations, which include a“bowtie,” a “W” and a “WI,” are shown in Hart, U.S. Pat. No. 6,192,061,the disclosure of which is hereby incorporated herein by reference.

Referring to FIG. 5, the second or active electrode 34 is integrallyformed from a suitable conductive material, which may, for example, be ametal such as aluminum, titanium, gold, platinum, or atitanium-aluminide alloy. The top surface 40 of the second electrode 34has a number of structures formed (e.g. machined) therein. Thesestructures include an elongate waveguide surface 42 that extendslengthwise of the second electrode 34 along an optical axis 44 of awaveguide channel forming in part by the elongate waveguide surface 42.As seen in FIG. 5, the elongate waveguide surface 42 is substantiallyZ-shaped with two parallel legs 46, 48 and a transverse leg 50. Alsoformed in the top surface 40 of the second electrode 34 are elongatevents 52 extending essentially the entire length of the elongatewaveguide surface 42 on both sides thereof. The elongate vents 52 areillustrated by hash marks in FIG. 5 for the sake of clarity.“Essentially the entire length” means to the extent possible by designlimitations. For example, the interior elongate vents 52A-D extend theentire length, but supports 58 are provided across the outer vents tosupport portions of a dielectric insert. These vents 52 may be formed bymachining material from the top surface 40 of the second electrode 34.Transverse vents 54 extend between interior elongate vents 52A-52D toallow for exchange of gas between the interior vents 52A-D and a volumeoutside the waveguide laser channel. The elongate waveguide surface 42has a non-linear section normal to the optical axis which can be viewedat 56 in FIG. 5 and is perhaps best viewed at 56 in FIGS. 3 and 6.Referring to FIG. 6, the non-linear cross-section 56 may be arcuate orconcave. The radius is chosen to eliminate higher order modes while notcreating an excessively non-uniform field. In one embodiment, a radiusof between about 0.4-0.0825 inch has satisfied both requirements. Alsodefined in the top surface 40 of the second electrode 34 are a number ofinsert supports 58 adjacent to the parallel legs 46, 48 of the elongatewaveguide surface 42 spaced lengthwise of the parallel legs 46, 48. Thesecond electrode 34 also includes a number of assembly holes 60 whichextend between the top surface 40 and a bottom surface of the secondelectrode 34.

The first or ground electrode 32 is typically made of the same materialsdiscussed with respect to the second electrode and likewise has a bottomsurface 64 into which an elongate waveguide surface 66 is formed, asbest viewed in FIGS. 3 and 6. Also formed in the bottom surface 64 ofthe first electrode 32 are dielectric insert channels 58 which extendlengthwise of parallel legs corresponding to the parallel 46, 48 of theelongate waveguide surface of the second electrode 34. A number of screwholes 69 extend through the ground electrode 32 from the planar topsurface 70.

The dielectric insert assembly 36 consists of four pieces. These piecesinclude two substantially symmetric triangular dielectric inserts 72 andtwo rail dielectric inserts 74. Each of the triangular dielectricinserts include alignment holes 76 to align with the assembly holes 60of the second electrode 34 and the screw holes 69 of the first electrode32 as illustrated in FIG. 2. As seen in FIG. 2, the dielectric insertassembly 36 is constructed and arranged to define side walls of theZ-shaped waveguide channel 38, as can also be viewed in FIGS. 3, 4 and6. The dielectric insert pieces can be made from a number of dielectricmaterials, for example, an alumina ceramic.

The waveguide laser assembly 14 is assembled by inserting the raildielectric inserts 74 into the dielectric insert channels 68 in thefirst electrode 32 and aligning the assembly holes 60 of the secondelectrode 34 with the alignment holes 76 of the triangular dielectricinserts 72 substantially as illustrated in FIG. 2. Ceramic bushings 80are inserted in each of the aligned assembly holes 60 and alignmentholes 76 then a screw 82 which has an inner threaded shaft bore 84 in anexteriorly threaded shaft 86 is received in a hole in the ceramicbushing 80 and threadably engages threaded holes 69 in the bottomsurface of the first electrode which are aligned with the assembly holes60 and the alignment holes 76. Once tightened, the screws 82 secure thewave guide laser assembly 14 in a sandwiched configuration with theZ-shaped waveguide channel defined by the non-linear elongate waveguidesurface 42 of the second electrode, the elongate waveguide surface 66 ofthe first electrode and the side walls of the triangular dielectricinserts 72 and rail dielectric inserts 74, as is perhaps best viewed inFIGS. 3 and 6. On one embodiment, the Z-shaped waveguide channel hasessentially a square cross-section normal to the optical axis, with thedistance between the electrodes being about 0.1 inch and the distancebetween the dielectric side walls being about 0.1 inch. The waveguidesurface of the non-linear waveguide has a radius of between about0.0825-0.4 inch, or distance of between about 0.03-0.005 inch betweenthe bottom and top of arcuate surface.

With further reference to FIGS. 3 and 6, in particular to FIG. 6, anelongate gap provides fluid communication between the Z-shaped waveguidechannel 38 and a volume outside the waveguide channel 38. Moreparticularly, the gap 90 extends between each vent 52A-D and theZ-shaped waveguide channel 38. This gap allows gas to flow between theZ-shaped waveguide channel 38 and the vents 52 to communicate with avolume 92 within the interior of the housing 12. In this manner,harmonic acoustic resonance is eliminated within the Z-shaped waveguidechannel 38. In addition, the gaps 90 provide an opportunity for anyparticles which enter the Z-shaped waveguide channel 38 to exit theZ-shaped waveguide channel 38 before striking one of the lasing optics.In essence, the elongate gaps communicating with the vents 52, 52A-D,combine the advantages of a free space laser with those of a waveguidelaser. In one embodiment, the gap is between about 0.05-0.01 inch.

Once the waveguide laser assembly 14 is assembled as described above,the waveguide laser assembly 14 is inserted into the housing 12 withoutcontacting any interior surface of the cavity 30. The waveguide laserassembly is inserted so as to bring the holes 69 into alignment with theholes 18 through a top surface 24 of the housing 12. The top surface 70of the first electrode 32 is then brought into abutment in a directionsubstantially normal to an inner top surface of the cavity 30.“Substantially normal” means there is substantially no lateral movementrelative to the inner surface of the top of the housing and the topsurface 70 of the first electrode which could scratch either surfacecreating particles. This may be accomplished by the screws 94 threadablyengaging the inner threaded bore 84 of the screws 82. In any event, oncein abutment and properly aligned, the screws 94 are tightened to providetight abutment between the top surface of the first electrode and thetop surface of the cavity 30 to promote efficient conduction of heattherebetween, grounding of the first electrode to the housing, and toprevent any relative movement therebetween. Referring again to FIG. 2,the holes 18 are countersunk so that the heads of the screws 94 onceengaged with the waveguide laser assembly 14 lie below the plane of thetop surface 24 of the housing 12. In this manner, the heat sinks 22 havemaximum surface contact with the top surface 24 of the housing 12 tomaximize efficient conduction of heat to the heat sinks 22.

Referring again to FIG. 4, mirrors 92 are provided to longitudinallydelimit the Z-shaped channel. A dielectric mirror 94 is provided at oneend of the Z-shaped waveguide channel 38 to allow emission of a laserbeam through the optical channel 96 in a manner known to those of skillin the art. Collimating and focusing optics, not shown, are opticallycoupled to the optical channel 96.

The RF-excited wave guide laser module 10 is assembled so that it isvacuum tight and once evacuated it can be filled with a gas mixtureincluding CO₂. The mirrors 92 and dielectric mirror 94 can then bealigned using the alignment screws accessible through the holes 20 in aconventional manner.

The waveguide laser assembly 14 may be inserted into the cavity 30 ofthe housing 12 without contacting the inner surface by use of a jig 100upon which the waveguide laser assembly 14 rests and then moving thehousing 12 in the direction of the arrow 102 to insert the waveguidelaser assembly 14 within the cavity 30. Thereafter, the inner threadedbores 84 of the screws 82 are aligned with the assembly holes 18 and thescrews 94 are brought into enthreaded engagement with the inner threadedbore 84 of the screws 82 as discussed above. Other ways of loading thewaveguide laser assembly into the cavity without contacting the interiorare also within the scope of the invention.

While not illustrated in the drawings, those of skill in the art willunderstand that an electric supply line will electrically communicatethe second or active electrode with a power source that provides analternating electric current at a frequency preferably in the radiofrequency range of the spectrum, so that the second electrode 34 and tothe first electrode 32 form a capacitance, and laser excitation takesplace in the Z-shaped waveguide channel 38. Inductor coils may beprovided in electrical parallel with one another and parallel to theaforementioned capacitance for distribution of inductance over thelength of the waveguide laser assembly as needed for efficient operationof the RF-excited waveguide gas laser module.

Referring to FIG. 8, by having the non-linear cross-section waveguidesurface 56 of the active electrode and the linear waveguide surface 66of the ground electrode defining in part the Z-shaped waveguide channel38, an even electrical field distribution illustrated by the field lines110 results which maximizes a good discharge formation and promotesorder mode suppression, thereby improving efficiency and the quality ofthe wave form. The gaps 90, by virtue of being located at a point ofminimal field strength, have a minimal effect on the dischargeformation. The gaps are also located at the point of lowest optical gainto minimize optical loss. Without being bound by theory, the metal tometal electrode surfaces are believed to facilitate electron transfer,promoting good plasma breakdown.

It should be understood any references made herein with respect todirections and relative locations are intended solely for explanatorypurposes in connection with the orientation of the laser components asdepicted in the drawings. However, other orientations of the componentsmay be used in applications of the invention disclosed herein.

While the invention has been particularly shown and described withreference to a number of embodiments, it would be understood by thoseskilled in the art that changes in the form and details may be made tothe various embodiments disclosed herein without departing from thespirit and scope of the invention and that the various embodimentsdisclosed herein are not intended to act as limitations on the scope ofthe claims.

1. A waveguide laser gas laser comprising: a first electrode; a secondelectrode; a dielectric insert sandwiched between the first electrodeand the second electrode, the dielectric insert comprising an elongateslot defining side walls; a waveguide channel having a length defined bythe side walls of the elongate slot of the dielectric insert, the firstelectrode and the second electrode; and a lengthwise gap extendingessentially the entire length of the waveguide laser channel between aside wall and an electrode, the lengthwise gap providing fluidcommunication between the waveguide laser channel and a volume outsidethe waveguide laser channel.
 2. The waveguide laser of claim 1 furthercomprising the first and second electrodes and the elongate slot of thedielectric defining a waveguide laser channel comprising at least twolinear segments with an angle therebetween.
 3. The waveguide laser ofclaim 1 further comprising the first and second electrode and theelongate slot of the dielectric defining a Z-shaped waveguide laserchannel.
 4. The waveguide laser of claim 1 further comprising thelengthwise gap being situated between a distal end of one of the firstand second electrodes and a side wall of the dielectric insert.
 5. Thewaveguide laser of claim 1 further comprising the second electrode beingan active electrode and the lengthwise gap being situated between adistal end of the second electrode and a side wall of the dielectricinsert.
 6. The waveguide laser of claim 1 further comprising a pair oflengthwise gaps extending essentially an entire length of the waveguidelaser channel.
 7. The waveguide laser of claim 5 further comprising apair of lengthwise gaps, with each lengthwise gap on an opposite side ofthe second electrode.
 8. The waveguide laser of claim 7 wherein thesecond electrode has a concave surface opposite the first electrode. 9.The waveguide laser of claim 1 wherein the lengthwise gap is formed at apoint where a side wall and an electrode would intersect.
 10. Awaveguide gas laser comprising: a first electrode having a firstelongate surface defining in part a waveguide laser channel extendingalong an optical axis; a second electrode having a second elongatesurface opposite the first elongate surface defining in part thewaveguide laser channel extending along the optical axis; a dielectricinsert sandwiched between the first and second electrode, the dielectricinsert comprising an elongate slot extending along the optical axishaving side walls defining in part the waveguide laser channel; and atleast one lengthwise gap extending essentially an entire length of thewaveguide laser channel between one of the first and second electrodesurfaces and the dielectric insert, each gap providing fluidcommunication between the waveguide laser channel and a volume outsidethe waveguide laser channel.
 11. The waveguide laser of claim 10 furthercomprising the first and second elongate surfaces and the elongate slotcomprising at least two linear segments with an angle therebetween. 12.The waveguide laser of claim 10 further comprising the first and secondelongate surfaces and the elongate slot defining a Z-shaped waveguidelaser channel.
 13. The waveguide laser of claim 10 further comprisingthe second electrode being an active electrode and each lengthwise gapbeing situated between the second elongate surface and a side wall ofthe elongate slot of the dielectric insert.
 14. The waveguide laser ofclaim 13 further comprising a pair of lengthwise gaps on opposite sidesof the second electrode.
 15. The waveguide laser of claim 13 wherein thesecond surface of the second electrode has a concave cross-section. 16.The waveguide laser of claim 10 wherein the lengthwise gap is formed ata point where a side wall and an electrode would intersect.